A lot of side channels along these lines were feared from BadBIOS (ultrasound was another one). But the whole BadBIOS thing was a lot of hypothesizing started by one security researcher with psychological issues (at the time). Lots of ideas about what could be done, but not a single shred of evidence that anything was actually being done.

(He briefly relapsed a few years later saying his Raspberry Pis had been loaded with implanted Ethernet jacks, and I had to spend some time teaching him about what Ethernet magnetics are... I hope I helped calm him down a bit that time)